Breast cancer is the most common cancer among women in the United States except skin cancer. It is estimated that each year, approximately 200,000 American women are diagnosed to have breast cancer. Depending on the type, stage of the cancer and other factors, patients having breast cancer may be treated with surgery, radiation, and other therapies. Surgery involves removal of breast lumps (lumpectomy) or all of the breast tissue (mastectomy). Radiation therapy uses high-energy radiation such as X-rays to kill cancer cells. Most patients receive radiation therapy after lumpectomy. The radiation destroys breast cancer cells that may remain in the area after the lumpectomy. Some patients have radiation therapy before surgery to destroy cancer cells and shrink the tumor.
In radiation therapy of breast cancer, accurate positioning and stabilizing of the breast is important to deliver a radiation dose to a treatment volume. Accurate positioning is particularly necessary during delivery of a boost dose to avoid a skin overdose and/or insufficient radiation dose to portions of the planned treatment volume. Breast tissue is pliable and readily deformable. Repeatable positioning of the breast presents difficulty. Maintaining a stable breast position during a single fraction often presents challenges.
The vast majority of radiation treatment of breast cancer is carried out with the patient in a supine position because of the ease of access and patient comfort. In this position, gravity depresses the breast towards the patient's torso and the breast tends to spread laterally over the chest wall. This makes accurate positioning of the breast more difficult and complicates the location of internal structures for boost dose. Treatment planning options are constrained by the greater proximity of the breast to the chest wall.
Experiments are being conducted in which the radiation treatment is carried out with the patient in a prone position, so that gravity pulls the breast away from the chest wall. This approach simplifies treatment planning while minimizing the radiation dose to the chest wall and lungs. However, in the prone treatment position gravity pulls the heart downward against the anterior chest wall which somewhat counters the benefit of gravity moving the pendulous breast away from the chest wall. Further, patient discomfort and access of the treatment beam to the breast present difficulties with current prone treatment configurations.